Attraction of THP-1 cells by SLFs-derived molecules. The culture medium of SLFs was collected after 6, 12 and 24 h with or without exposure to the NTHI lysate, respectively. Migration assays show that the conditioned medium of NTHI-exposed SLFs highly attracts THP-1 cells compared to that of NTHI-unexposed SLFs (A). RFU: relative fluorescence unit. Invasion assays show that NTHI-induced SLF-derived molecules enhance invasion of THP-1 cells (dark and solid) to the extracellular matrix on the semi-permeable membrane with pores (light and open) (B). It is noted that NTHI lysate per se does not affect migration and invasion of THP-1 cells, compared to the NTHI-induced SLF-derived molecules (C). *: p < 0.05. The experiments were performed in triplicate and repeated twice. Values are given as the mean ± standard deviation (n = 3).